Steam Turbines - Part B Flashcards
What is a Governor?
Controls speed of the turbine automatically under varying load conditions.
What is a Acceleration Governor?
A safety feature that quickly closes the steam admission valve (SAV) in case of sudden removal of the load to a generator. This governor relies only on acceleration and is used as a safety feature, not to contol turbine speed. When activated, the turbine slows down; once the turbine is under control it opens the SAV.
When does the Acceleration Governor close the admission valve?
Only during high acceleration.
What is the Overspeed Trip?
A mechanical/mechanical hydraulic activated system that is used to shut off steam to the turbine in an overspeed situation.
What is this?
Label it.
- Overspeed Trip
How does an overspeed trip work?
During normal operation, a spring holds the tripping lever in position. Overspeed trips at 110% to 115% of operating speed. Centrifugal force overcomes the spring tension moving the bolt to trip position and strikes the overspeed mechanism which in turn closes the stop valve. Then the blowdown valve opens to relieve internal pressure back into the condenser.
Do some turbines have more then one Overspeed Trip?
Yes
How do you reset a Overspeed Trip?
Manually
Where do you find the Main Stop Valve?
In the steam system before the steam chest.
When the overspeed trip activates it ____________.
It closes the stop valves and stops the flow of steam to the turbine.
What is the purpose of a coupling?
To transmit power from the prime mover to the driven piece of machinery.
Most power generation turbines use what kind of couplers?
Solid flange coupling
What do you have to be mindful of with a solid flange coupler?
That for maximum power transfer and minimum shear stress, the bolts must fit in the holes without clearance.
What do you have to check for in a casing drain before start up on a turbine?
Water.
At what percentage of overall speed does the Overspeed Trip?
110%-115%
What is the strongest part of the turbine?
The steam chest bolted to the turbine casing.
What is a Dummy Piston?
A balance piston which is part of the rotor with several stepped diameters that the steam pressure in the turbine can push against to counteract the thrust.
Do impulse sections create thrust?
No, not much.
What is a Dual Flow Rotor?
A method to control thrust in a turbine. Rotors reaction blades are shaped like and hour glass and the steam is fed through the center radiating outward
What does a boiler do?
Provides high pressure steam.
Why are tubines found near water?
So that they have a large source of cooling water.
What are large generators cooled with?
Hydrogen
What are small generators cooled with?
Air
What ia a turning gear used for on a turbine?
Is used to rotate the rotor slowly long before start-up so that any bow in the rotor due to sag can be removed before the turbine is started.
Is also used when the turbine is initially heated to allow even heating.
Also rotated during shutdown to prevent sag.
